Vehicle control systems which reduce the wheel slip to a value appropriate for ensuring traction and driving stability by building up brake pressure on the overspeeding drive wheels and applying a stronger drive torque to the wheels with tire contact are known from the prior art. These systems are available both for two-wheel drive and all-wheel drive vehicles. These vehicle control systems are called traction-slip control systems (TCS), or also “Electronic Differential Lock”, “Automatic Stability Control,” and “Traction Control System”.
Two designs have to be differentiated with respect to traction-slip control systems: traction-slip control and brake traction-slip control or brake traction-control systems. The first, i.e. traction-slip control system, additionally throttles the engine torque in certain situations in order to keep the load on the brakes as low as possible. The brake traction-slip control systems become effective only through automatic braking intervention. In the following, “TCS” refers to all feasible traction-slip control systems, i.e. those with and without intervention in the engine management.
Traction-slip control systems basically are configured for primarily level ground and road usage characterized by an at least approximately identical friction coefficient on both sides.
When an all-wheel drive vehicle without axle differential lock drives over a diagonal furrow, causing the diagonally opposite front wheel and rear wheel to lose contact to the ground, these two wheels spin and so prevent any drive torque from being applied to the two wheels touching the ground (the two opposite wheels along the other vehicle diagonal). Since the vehicle Is twisted considerably, this situation should be overcome as quickly as possible. For this purpose, strong tractive power is necessary to move the vehicle. An uphill road or an abrupt obstacle, for example a stone, lying in front of one or several wheels makes the situation even more difficult.